1. Technical Field
The invention relates generally to micro-scale or nano-scale device fabrication, and more particularly, to methods for forming a mask with self-aligned, self-assembled sub-lithographic features.
2. Background Art
A mask is a glass or quartz plate containing information about the features to be printed on a semiconductor wafer. This information is contained in variations in the plate that create differences in topography, transmittance or phase. The mask is used as a master template to transfer design images onto a wafer either through exposure to radiation (lithography) or through direct contact (nanoimprint). The mask is an intermediate step created to transfer the design to the wafer image, so the mask features are adjusted to create the desired wafer image.
A simple form of altering the mask data is to change the size or shape of the mask feature so that the printed wafer feature size matches the desired feature size and shape. A more complex change to the design is to add sub resolution features (SRAFs) that are too small to transfer to the wafer, but improve the printability of design features. The result is a large increase in very small features that are placed around design features. These small features challenge the resolution of the standard mask fabrication process. If small features are desired in a different material from the main feature, 1st-to-2nd pass pattern alignment is inadequate. These features also consume time in many ways. It takes time to generate sub resolution features and output mask data. The final mask data set is significantly larger than the input design data. The larger the data file size of the mask data, the slower the transfer of data, the slower the fracturing of the data into write-ready form, and the slower the mask fabrication process. If a problem is found with the sub resolution feature placement or size, the entire data processing sequence must be initiated again.